Casting processes, such as, for example, investment casting (also known as lost wax process), plaster mold casting, and lost foam casting, have been developed as a method for making a casting with better dimensional accuracy than typical sand mold casting.
Among others, the lost foam casting is most suitable for forming a hole (referred to as a “cast hole”) in a casting by casting. In the procedure of the lost foam casting, firstly, a casting pattern is obtained by applying a mold wash on the surface of a foam pattern. After the casting pattern is embedded in foundry sand, molten metal is then poured into the casting pattern, so that the foam pattern is lost (vaporized) and replaced with the molten metal. Finally, a casting is obtained by casting (solidifying) the molten metal.
Prior art documents disclosing the lost foam casting described above includes, for example, Patent Literature 1. Lost foam casting disclosed in Patent Literature 1 sets a casting time for casting based on the modulus of a pattern (i.e., volume of pattern÷surface area of pattern). This lost foam casting allows for the setting of accurate and precise casting time.
FIG. 15 is a schematic cross-sectional view of a cast hole formed by lost foam casting. When forming a cast hole using the lost foam casting, a mold wash 24 is applied to the surface of a foam pattern 22 having a hole 23 and thus a casting pattern 21 is made, as illustrated in FIG. 15. The hole 23 corresponds to where a small hole is formed by casting. By embedding the casting pattern 21 in foundry sand 25, the foundry sand 25 is placed around the casting pattern 21 and in the hole 23. Molten metal is then poured into the casting pattern 21 and the foam pattern 22 is replaced with the molten metal. Finally, a casting is obtained by casting (solidifying) the molten metal.